The present invention relates to electronic blood pressure measuring devices and more particularly, to maximum a pulse wave amplitude calculating system and operation method for electronic blood pressure measuring devices which can compensate for incorrect measurements of the maximum pulse wave amplitude--that is, the mean blood pressure--due to oscillation noise interference.
A prior art electronic blood pressure measuring device based upon the oscillation method includes a cuff which is wound around the upper arm of the person whose blood pressure is to be measured, a pressurization pump for pressurizing the cuff, an exhaust valve for exhausting the air within the cuff, a pressure sensor for detecting pulse waves and cuff pressure, an A/D converter for converting analog signals received by the pressure sensor into digital signals, and a microcomputer which receives pulse wave amplitudes and the cuff pressure from the converted digital signals, and calculates the maximum/minimum blood pressures by processing the information. In such a conventional electronic blood pressure measuring device, the method for calculating the maximum and minimum blood pressures from the cuff pressure and pulse waves is as follows.
Pulse waves are detected by the pressure sensor when the cuff pressure is gradually decreased after the blood flow in the patient's artery was momentarily stopped by pressurizing the cuff to a certain level.
The amplitudes of pulse waves, as shown in FIG. 3, form a graph curve which, with each amplitude, gradually increases until the maximum pulse wave amplitude Pn is recorded, and then diminishes over time.
In general, the maximum blood pressure pulse wave occurs at the cuff high pressure side corresponding to 50 percent of the maximum pulse wave amplitude, and the minimum blood pressure pulse wave occurs at the cuff low pressure side corresponding to 70 percent of the maximum pulse wave amplitude.
It is therefore important in the measurement of the patient's max./min. blood pressures to detect and identify the correct maximum pulse wave amplitude from among the numerous pulse wave components.
However, if an oscillation noise interference having a greater amplitude than the actual maximum pulse wave amplitude is present, the oscillation noise interference may be incorrectly identified as an actual maximum pulse wave amplitude. Because this incorrect maximum amplitude can cause an erroneous measurement of the max./min. blood pressures, all oscillation noises become important factors in potentially diminishing the accuracy of electronic blood pressure measuring devices.
The causes of such oscillation noise interference are as follows.
Even though the patient's heart generally generates regular pulse waves, sometimes irregular pulses may be included among them so that they create the possibility they will be incorrectly identified as maximum pulse wave amplitudes. Further, an oscillation noise interference may be caused by a momentary muscle jerk of the patient being evaluated.
Further, oscillation noise interference can be caused by the conscious or unconscious trembling of the patient being measured.
These kinds of oscillation noises can be identified as actual maximum pulse wave amplitudes when they are detected among the regular pulse waves sensed at the cuff.
FIG. 3 shows one typical cycle of pulse wave amplitudes sensed at the cuff when the cuff pressure for measuring the patient's blood pressures is decreased, where Pn represents the maximum pulse wave amplitude.
FIG. 4 illustrates a situation where a pulse wave amplitude Pa, made by any of the aforementioned oscillation noise interference, is larger than an actual maximum pulse wave amplitude Pn. Accordingly, the max./min. blood pressures are incorrectly measured because the microcomputer analyzing pulse wave components identifies the pulse wave amplitude by the oscillation noise Pa as the maximum pulse wave amplitude Pn.